Lots of options on this one, from very cheap to the more expensive, including rock between pad and rotor, rock between dust shield and rotor, stuck caliper, bad wheel bearing, even a failing output shaft.
How about a little more info on the "squeak"?
Is is rhythmic (as is in squeak, pause, squeak) that decreases in time intervals as the car moves faster? (This might be a rock between the pad and rotor or even the dust shield and rotor.) Rock issues usually resolve themselves (rock crumbles) and if the shop really did take things apart, this is unlikely.
Is there a lot of heat coming off the rotor/brake assembly? Don't touch it--just put your hand up to the wheel and compare to the other side. Most likely a a stuck caliper as already noted by Kgolf.
Is it more noticeable around corners or in turns? And if you jack up the car and get the wheel off the ground is there any play in the wheel itself? (Shouldn't be.) Does is grind or make noise when turned by hand? If so, it's probably a bad wheel bearing (something that should be addressed asap).
Lastly, if it's none of those, it might be the output shaft, cracked CV, etc. Any visible sign of damage or cracks or seal leaks? (Like this.)
Shop should have checked all these possibilities, but since the issue remains, I wonder what they actually did. Either take it back to the shop and tell them to try again, or find another shop.